LEITZ NPL 100x 0.9 infinite

[clipi]

Hello.

I just got this Leitz NPL 100x 0.9 lens. Can anyone tell me if it requires oil inmersion? What advantages has over the EF 100x 1.25NA
Giving the 0.9 aperture can I use a normal condenser to achive Dark field?
Thanks!

[Hobbyst46]

Hello. What advantages has over the EF 100x 1.25NA
Giving the 0.9 aperture can I use a normal condenser to achive Dark field?
Thanks!

In theory, any 1.25NA objective would give a better resolution, by a factor of 1.25/0.9 = 1.39, than any 0.9NA objective. Provided they are used with the same wavelength of illumination light.
To achieve good darkfield with a 0.9NA objective, one needs a dedicated oil condenser, that is, the front (top) lens of the condenser should be oiled to the slide.
Alternatively, there are condenserless tricks, like LED rings. They are mostly DIY, not commercial. Overall, a darkfield with an objective of 0.9NA and no dedicated condenser is still a challenge, at least in the amateur world.

[clipi]

Hello

Thanks for the info. I think this is a Dry condenser used for metalurgical observation. But I don´t have
any idea of how is going to work for Biological observation. It is substantially more expensive than the 1.25 NA objective.
Now I don´t understand one thing. I read that with Objectives with Iris you can reduce that NA aperture to achive Dark Field without needing
special condensers is that correct?

Thanks

[Hobbyst46]

Hello

Thanks for the info. I think this is a Dry condenser used for metalurgical observation. But I don´t have
any idea of how is going to work for Biological observation. It is substantially more expensive than the 1.25 NA objective.
Now I don´t understand one thing. I read that with Objectives with Iris you can reduce that NA aperture to achive Dark Field without needing
special condensers is that correct?

Thanks

I am not familiar with Leitz objectives. However:
1. Often metallurgical objectives - epi-illumination that is - have a larger diameter thread than ordinary microscope objective (RMS). So you will need a separate nosepiece for the metallurgical objective, or alternatively, if using a single nosepiece for all objectives, you will need collars for the threads of the ordinary objectives.
2. Metallurgical objectives include a "sleeve", through which light passes through the objective onto the specimen. This sleeve is external to the objective lens itself, so the objective as a whole is thicker than ordinary, trans-illumination objective. And indeed more expensive.
Unless you will use epi-illumination, why pay for metallurgical objective...?
3. IF, by means of an iris or similar device, the NA of the objective is significantly reduced below the NA of the condenser, then in principle you can have darkfield with that condenser.

[clipi]

This is a picture of the objective..
Seems to have a normal thread.

[Hobbyst46]

Metallurgical objectives are usually used dry, without immersion.
It is infinity corrected optics, but the /o mark I do not recognize. No coverslip is used, perhaps?
About the thread diameter - I might have been wrong, the photo does not provide dimensions.

[zzffnn]

This is a picture of the objective..
Seems to have a normal thread.

It MUST be used dry without cover slip at that high NA of 0.9.

[wporter]

zzffnn is right, that's what the "0" means: must not use a cover slip. As opposed to "-", which means a coverslip is optional.

The older metallurgical scopes (1960s & before) did not have light-path sleeves around the objectives, but used a beamsplitter to send the light down the center (optical axis) of the objective to illuminate the specimen. Probably this approach was eventualy ditched due to flare and glare, etc.

[Hobbyst46]

Thanks zzffnn and wporter!
I have used a Nikon metallurgical Optiphot (1 or 2 I do not know), so possibly more modern optics than the objective shown by the OP.